Readers will be the first to put me right, but I do not know of a British church dedicated to St Valentine, the third-century Christian martyr associated, by historical accident, with the sending of valentines. If there is, I wonder what it looks like? Can the idea of love be represented or sublimated successfully in stone or bricks and mortar? I don't mean happy suburban homes with roses around the Kentucky Fried Georgian door, but monuments to grand passion.

Architects and their patrons have tried, but these monuments have usually been erected to lust rather than love, although how far the two can be separated has never been clear.

Brighton Pavilion is clearly a pleasure dome; every voluptuous billow of the Prince Regent's seaside palace speaks of lubricious summers spent among a soft mound of silk pillows.

But, where can you find the architecture of pure love, the sort John Betjeman had for Peggy Purey-Cust (and recorded in "Summoned by Bells") or I had for Susan Connolly, who smelt so wonderful, when I was five? The most famous example is the Taj Mahal, that astonishing white marble mausoleum on the Jumna River in Agra built between 1632 and 1643 by the emperor Shah Jahan in memory of his beloved wife, Mumtaz Mahal. Taj Mahal means the "crown of buildings" in Urdu. Members of royal families, noble peasants and hordes of tourists have come this way for 350 years hoping to share in the latent magic of this peerless Mogul building. Mostly they experience crowds of people, although early on a February morning in the pink rose of dawn and before the coaches and the trains from Delhi arrive, the Taj is a truly moving sight.

I am not sure if this has anything to do with the love that Shah Jahan bore Mumtaz Mahal, for I have felt an equal sense of delight - that same involuntary shudder up the spine - when looking once from the hill above the Thames at Dorchester to Didcot Power Station. I hope this doesn't sound mad, but when the sun catches those great cooling towers and the plumes of fleecy white steam that rise so gently from them, south Oxfordshire seems a strangely heavenly place. Love and power stations are odd bedfellows, I agree, but what I am struggling to say is that our experience of delight in architecture and buildings in the landscape has everything to do with their form and setting and the light that plays against them and probably nothing at all to do with the fact that a particular building might have been inspired by the great love two people bore one another.

Grand passions may be played out in the least likely settings, whether the "high-rise horrors" of tired newspaper headlines or the grand country houses of Brideshead-fuelled fancy. My favourite, though, is a Gothic Horror house in Hampstead that once featured briefly in John Betjeman's TV documentary Metroland. It was called "Agapemone" (or the House of Love), and although the Greek word "agape" has long been used to denote to Christian love (as in God's love for us), this "Agapemone" was a house in which a Victorian CofE priest announced that he was Jesus Christ and shared his love in carnal fashion with a number of susceptible young women.

This, though, is not a very romantic example of a monument to love.

As a counterpoint, I offer another Gothic Revival house, this time St Marie's Grange, Salisbury, a Wilhelmina fancy designed by Augustus Northmore Welby Pugin for his first wife who died, tragically, very soon after this extraordinary home was completed. Pugin had married, he said, a perfect "Gothic wife" and they were to have led a perfect Gothic life in Wiltshire. Today, although the house survives, it has been much altered and is no longer as whimsical and as striking as it would have seemed in the 1830s.

Who knows of other and better examples? I would love to know about them.